Greetings everyone! I've been working a lot with my new (to me) 1990 525i and want to throw some upgrades at it. What I've been focusing on recently is swapping out the differential. I think I want to lower the ratio, which I know sounds counterproductive, but my reasoning is that the current final drive is 3.75, and first gear is 3.84. Together making first gear just about useless for anything faster than 10-15mph. SO if I were to drop the ratio to around 3 I would get a lot more out of first gear. Does anyone know what differentials will bolt right up in place of mine, or even with some minor modifications? The ratio of the 1987 E30 325 and E28 528e is 2.93, could this fit my e34? I would love to hear everyone's opinion on this swap, since when talking diff swap, you usually go up instead of down. Lastly, will changing the ratio mess up the speedometer reading? Thanks in advance!

south26

12-30-2012 08:38 PM

The e30, e28, e24, e23, z1, will not work. I believe the only diffs that will work on the e34 are the e34s and the e32. (maybe the e38). The 525i has a medium diff like the 535i, and 530i. I believe the output flanges on the 525i are different so you would have to change those on diffs from the other cars.
The one from the e34 540 will be different since it is a big diff like the e32.

The e30, e28, e24, e23, z1, will not work. I believe the only diffs that will work on the e34 are the e34s and the e32. (maybe the e38). The 525i has a medium diff like the 535i, and 530i. I believe the output flanges on the 525i are different so you would have to change those on diffs from the other cars.
The one from the e34 540 will be different since it is a big diff like the e32.

Half right half wrong. the E30/E28 etc diffs will not bolt in directly, you will have to swap the back cover plate over which unbolts. the body and inside of the diff is the same. seeing as you already have an E34 diff, buying an E28 etc diff is a possible solution. just make sure its a medium case diff. one from a 6 cylinder E32 or E34 will bolt straight in

if your car was a V8 E34, then it would have a large case diff, and your only option would be an E34 540i or E32 740i/740iL/750iL diff

Microtesties

12-30-2012 11:48 PM

Quote:

Originally Posted by south26
(Post 7280274)

The e30, e28, e24, e23, z1, will not work. I believe the only diffs that will work on the e34 are the e34s and the e32. (maybe the e38). The 525i has a medium diff like the 535i, and 530i. I believe the output flanges on the 525i are different so you would have to change those on diffs from the other cars.
The one from the e34 540 will be different since it is a big diff like the e32.

Pretty sure the diff in the V12 750 is the large case and will not work without substantial modification.

south26

12-31-2012 07:58 AM

Quote:

Originally Posted by _Ethrty-Andy_
(Post 7280381)

Half right half wrong. the E30/E28 etc diffs will not bolt in directly, you will have to swap the back cover plate over which unbolts. the body and inside of the diff is the same. seeing as you already have an E34 diff, buying an E28 etc diff is a possible solution. f

Sorry, the body is not the same, and the input from the drive shaft is different. The insides might be the same. I just looked at one from a e34 535i and from a e28 528e and they are different. They are bolted in completely different. Also the e30 has 2 different types of diffs. The 4ers have a different diff that can not be used on the 6er e30s or the e28.